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The Collation

Pi(e) day, represented

Pi given as a ratio
Pi given as a ratio

March 14th is Pi(e) Day, and this year we get an extra two digits (this year’s date being, in the American style, 3/14/15, taking us through the first 5 digits of pi). While many people (including our culinarily-inclined staff here at the Folger) celebrate this day with sweet (and not-so-sweet) pastries, I wanted to bring the day back to its roots, and explore the mathematical side of Pi Day.

Symbolic algebra is something that most of us take for granted today; it’s how we are taught in school from very early on, and it becomes so ingrained in our language that the symbols (and their attached meanings) have started to move out of the realm of mathematics and into our everyday lives, as anyone who has ever used a character-limited media like Twitter knows well.

Tweets using mathematical symbols in place of words

using = as equal to and != as not equal to

But where did this start? When did the symbol = come to mean “is equal to,” + mean “plus”, and when did the ratio of a circle’s circumference to its diameter get called by the Greek letter pi, and then when did it shift to the actual Greek letter π?

For the answer in English, at least, we have to begin with Robert Recorde. In between being a physician and the administrator of the Bristol mint, Recorde was a mathematician. His first publication, The Grounde of Artes (1543; STC 20797.5), was a basic introduction to arithmetic, written in dialog form, that was enormously popular and was reissued many times, for over a century after his death. 1 

  1. Stephen Johnston, ‘Recorde, Robert (c.1512–1558)’, Oxford Dictionary of National Biography, Oxford University Press, 2004; online edn, Jan 2008 [http://www.oxforddnb.com/view/article/23241].
  2. Can you imagine trying to write that out in prose?
  3. Insert your own Life of Pi jokes here.
  4. Ruth Wallis, ‘Jones, William (c.1675–1749)’, Oxford Dictionary of National Biography, Oxford University Press, 2004; online edn, Sept 2012 [http://www.oxforddnb.com/view/article/15104]

Comments

We can do this again next year, because 3.14159 rounds to 3.1416.

William Ingram — March 12, 2015

Reply

Interesting also that the Romans seemed quite happy to adopt and use the Greek word ‘diametros’ but balked at ‘perimetros’, preferring their own ‘circumferentia’ for the latter. So today we’re stuck with one Greek and one Latin word for the two aspects of π, even though we still use the Greek letter ‘π’ instead of ‘c’ for the circumference of a circle whose diameter is 1.

William Ingram — March 12, 2015

Reply

Thanks so much for this post, Abbie. It got me thinking about type supply and whether you noticed a correlation between printers who use π in mathematical treatises and those who were already printing books that required Greek type sorts.

The other thing that occurred to me is that original research about the history and use of special characters (like π, ¶, etc.) in printing is only possible through contact with physical books or the browsing of digital resources like EEBO since such digital corpora/repositories do not (yet!) permit us to search directly for these special characters. This said, all the more credit to you for your work here!

Claire M. L. Bourne — March 13, 2015

Reply

Fascinating blog entry – thanks. It would be useful to hear some further remarks on the “underground” status of math in early modern thinking and, more generally, how this sort of applied mathematics relates to the enormously influential but still poorly understood or appreciated neo-Pythagorean doctrines of the age.

psi — March 14, 2015

Reply

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